The subject invention relates to character printing apparatus and particularly to apparatus for transferring character data between a data source such as a word processor font and a high speed printer such as a laser printer.
In conjunction with a scanning copier, the invention allows for receipt of graphical characters in any order, preserves the fixed scanned printing regimen during printing and eliminates the need to provide storage of a full graphical image of what will be printed. Instead, storage for only a small fraction of the complete image is required.
The invention may find use in devices in which an ordered raster scan image is to be created from an initially unordered set of graphical characters. Graphical characters are considered to be condensed representations of parts of a graphical image, which may describe ideographs, text, or other graphic objects, each with a specific or implied coordinate at which it will be placed in the final image. The preferred embodiment of the invention is in a copier which prints an image by scanning line by line, each line adjacent to the next, while receiving data from a host which produces characters in arbitrary textual order, such as a typical word processing system might send to a typewriter attached to it.
In such apparatus, it is desirable to transfer data from the font format to a random access storage facility where it can readily be extracted in real time in pixel format to accommodate the successive line scanning of the printer. Because of the speed of the printer, constraints are placed upon any device operating in real time. The complexity of the operations involved and the real time constraints present a challenge in designing an economical interface controller.
The controller must satisfy the major constraints that (1) the printer is supplied with print data at each request, (2) the building of characters keeps the limited controller memory supplied with data, (3) the building process is not permitted to overrun the controller memory area from which data is being extracted for printing, and (4) the processes all operate in real time.
It is therefore a major object of the invention to provide controller apparatus for a high speed printer which satisfies the foregoing constraints, while reducing hardware costs.